FIELD OF THE INVENTION
The invention relates to a device for controlling suction air or vacuum which, more particularly, is applied to suction openings of a cylinder of a printing press, and a method of actuating the control device. In particular, the invention relates to a device for opening up and closing off suction lines to sheet transfer drums having suction grippers in sheet-fed rotary offset printing presses.
Suction-air controlling devices of this general type offer a possibility of guiding small-format sheets of printing stock on a variable-format cylinder disposed between two printing units and equipped with a row of suction grippers designed for the maximum format, aspiration of faulty air through openings of the suction grippers not covered by the small-format sheets of printing stock being thereby avoided. In this manner, high energy consumption and undesirably low efficiency, respectively, the aspiration of relatively large contaminating particles, and increased noise emissions during printing press operation are avoided.
In the Published, Non-Examined German Patent Application (DE-OS) 42 17 851, a device for feeding and blocking or checking suction air in turning drums is proposed wherein, as a central blocking element, there is provided a control shaft, which is guided and rotatably disposed in an axial bore and has control channels arranged on the circumference thereof. The control channels correspond with vertical bores formed in a rocker shaft and a crossbar and terminate in the suction heads.
A disadvantage of this arrangement is that it requires either a special manufacturing process, wherein an epoxy resin is introduced into the axial bore, or a conventional but very expensive or cost-intensive production process because of the high precision required.
The invasion of contaminants, especially paper particles, into blocking devices or suction-air or vacuum controls in machines, i.e. presses, for processing printing stock is unavoidable when in use. If these contaminants become stuck in sliding guides and air ducts, they can cause functional impairments, such as seizing, binding upon actuation, or plugging up of small-diameter air ducts. In this respect, such devices, for example, like those described hereinabove, which require very high precision because of their construction, are especially vulnerable. Because there is only one sealing point in the vacuum control, contamination aspirated from a plurality of suction heads can lead to an accumulation at this critical point, especially since the components that form the sealing point are moved only seldom towards one another, e.g., upon a change of format, and thus any contaminants that have become stuck there are barely able to be detached. Consequently, maintenance intervals have to be shorter, and cleaning and the elimination of problems always involve extensive dismantling of device elements.
The Japanese Published, Non-Examined Patent Application JP 4-153039 describes a suction apparatus at the transfer cylinder of printing presses which contains a first tube having a wall wherein openings are formed that are assigned to air ducts discharging into suction openings. By rotational actuation of the first tube, which is disposed in a second tube, the air ducts branching off from the second tube can be opened and closed, causing the openings in the first tube to coincide with the intersection openings of the branching air ducts in the second tube. Because, in this apparatus, the diameter and thus the circumference of the tubes which are formed with the valve openings cannot as a rule be selected to be arbitrarily large, for reasons of structural space, the number of suction openings that can be blocked off and disposed over the cylinder width is very restricted. Moreover, this apparatus again has the problem of malfunctions caused by soiling.